I want to have a simple warning pop up when the "Pickup date" (a custom field) is today, and it is 3:00pm or later to say that deliveries after 3:00pm need to be scheduled the following day, what is the easiest way to accomplish this?

We can use a scheduled script for it.

Is there by chance an example online that I could try and follow?

@Joe Morreale Do you want the alert to show on specific pages / record types / transactions?

It would be a case that we want it to show on. We use them for transportation